In conventional transformer structures one or more windings each having a predetermined number of turns are wound about a ferromagnetic core. By applying an alternating current to one of the windings a changing magnetic flux is produced in the core generating an electromotive force in the winding(s) with a potential difference occurring between each turn. The potential differences between the turns are cumulative along the length of each winding. The output of the transformer is taken across a portion or all of the sole winding, if an autotransformer having a single winding is used, or across a portion or all of a secondary winding, if the transformer consists of primary and secondary windings. In order to vary the voltage output of the transformer an inductive regulator may be used which effectively varies the magnetic coupling between respective windings or a slidable brush arrangement may be provided in which a brush is slidable along exposed segments of the surface of the winding in a direction transverse to its turns. When the sliding brush rests on one conductive segment of the winding, a current path to the electrical load is established. If the brush rests upon two exposed segments at the same time, an additional current flow path is established in the portion of the winding between the two exposed segments and through the brush. Such a current which flows through a portion of a winding is a short-circuit current, which is undesirable and in effect can lead to the destruction of the transformer. If the brush does not contact an exposed segment of a winding, an open circuit exists and then no current is supplied to the load.
Advantageously, as described and claimed in my application Ser. No. 890,523 entitled "Variable Transformer Method and Apparatus for Preventing Short-Circuit Current Flow", now issued as U.S. Pat. No. 4,189,672, in order to make a smooth transition and provide a continuously adjustable alternating current voltage to the load, a plurality of brushes may be provided for contacting exposed segments of the turns of the winding along separate traverse paths, with the brushes being moved simultaneously to insure that one of the brushes is always in contact with a winding in order to deliver alternating current (AC) to the load. The short-circuit current flow is prevented, when each brush is in contact with respective exposed segments of a winding at different potentials, for both brushes are connected to the load through circuits containing rectifier means. Therefore, a respective one of the two brushes which is at the lower potential is isolated from the alternating current load circuit by the non-initiation of conduction through the respective rectifier means.